Metabolic adaptations resulting from exercise programs or environmental conditions such as high altitude or cold temperatures are widely characterized at the level of the whole-animal (or human). Not as well understood, however, are the biochemical and molecular mechanisms of such responses. The long-term goal of this work is to elucidate mechanisms that underlie these important forms of metabolic adaptation. Improved understanding of the biochemical mechanisms responsible for regulation of metabolism will yield insight into the bases of various forms of metabolic adaptation, including the health benefits resulting from regular exercise, and metabolic imbalances such as in obesity. Mammalian acclimation to cold temperature is accompanied by the following metabolic adjustments: a) a chronic increase in overall flux through the catabolic pathways for carbohydrates and lipids, b) an increase in acute maximum metabolic rate, and c) potential shifts in the relative contributions of carbohydrate and lipid oxidation to overall catabolism. This integrative study will measure the magnitude of these metabolic responses in mice and then attempt to identify the responsible mechanisms at the level of biochemical adjustments and patterns of gene expression associated with metabolic shifts. An important contribution of the project is the measurement of the effect of cold acclimation and exposure on properties of every enzyme in glycolysis. These results will help resolve a current controversy between classic models of biochemical regulation and alternative models known as metabolic control theories. The specific aims of the project are to determine the effect chronically increased metabolic demands on 1) the relative contributions of carbohydrates and lipids to total metabolism, 2) important properties of key enzymes representing several catabolic pathways (including all 10 glycolyticenzymes), 3) the mechanism by which increased flux through a representative pathway, glycolysis, is regulated, and 4) the expression of thousands of genes in key effect or tissues, measured simultaneously using cDNA microarrays.